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Those who assiduously follow all-things-Ivorybill likely already know that one of the recent topics of discussion over at IBWO Researchers Forum has been potential drumming (or tapping) patterns for the Ivory-bill possibly heard in the field by searchers or recorded in Cornell's original (and only confirmed) soundtrack of Ivory-bills from the Singer Tract (1930s), available here:
http://macaulaylibrary.org/audio.do?id=6784
Bill Pulliam weighs in with his thoughts on the matter here.
I'm all for pursuing all leads and forms of analysis. My only precaution being that the Cornell recording represents a single example from a miniscule sample of birds at one isolated location 70 years ago, and I'm not willing to assume that the tape is NECESSARILY technically representative of remnant birds left today in other parts of the country, separated by several generations from the birds recorded... BUT, that tape is all we got, so of course, by all means use it (and I think there is reason to believe that rapping or drumming patterns would change less over time than "kent" sounds might... still, very small sampling size). So have at it.
The other focus of attention lately over at the IBWO Forum has been a recent possible (brief) sighting claim for 2 Ivorybills in the Congaree (S.C.) by one of the independent searchers there. The Cornell search team is scheduled to be in S.C. in mid-March anyway; we'll see if the latest claim gets them there any sooner. S.C. remains near the top of everyone's list for best potential IBWO habitat in the entire Southeast; whether there are birds there to utilize it, time will tell.
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10 comments:
Why would you expect either drums or vocalizations to change in such a short period of time? Woodpecker calls and drums have never struck me as especially plastic or variable. Unless there was some kind of really hard selection on it (and why would there be sudden dramatic selection to change the nature of drums or calls?) I don't see any reason to expect them to have changed. Geographic and individual variation is another matter, but we're just stuck with that and there's no a priori evidence that it existed to any significant degree. Common woodpeckers give a clue; a Pileated in California, Michigan, Tennessee, or Florida is pretty much all the same as far as drums and calls are concerned. And I don't ever recall coming across a woodpecker of any species that had a notably aberrant call or drum (unlike, say, Towhees I have known that sang Carolina Wren songs, etc.)
I think the more important gist that CT was trying to get across is that the one IBWO recording we have is unlikely to encompass even the range of individual variation in drumming. Hence, there is muuuuch we don't know.
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Anon: Of course there is much we don't know; there is ALWAYS much we don't know about EVERYTHING; that's a given. So let's focus on what we do know; that is my point. Sure, it's only one pair of birds and only 5 minutes of audio; but the odds are, they are probably a typical pair and that 5 minutes probably represent typical vocalizations and rapping. The full range? Of course not. But, a sample of common, typical behavior? Probably so. There's only a 5% chance that they fall outside of the 95% confidence range for typical behavior. The implication/suggestion that these things would have changed significantly in the 10 or so generations since this audio was made seems quite out of the blue.
Something we do know: that the Ivorybill had a loud fast double rap, apparently similar to that of the Pale-billed, that is not heard in this recording. A pair of Pale-billeds under similar circumstances would have probably been double-rapping at each other almost continuously; from this we might conclude that though the Ivorybill had a similar double rap, it might not have actually used it nearly as often as some other Campephilus species and this slower rapping might be the primary contact call, at least between members of a pair. This is significant, especially since the fast double rap has been a primary focus of contemporary audio searches for the bird. It's a hypothesis, based on a small sample, but it's based on simple observations and hard evidence.
The implication/suggestion that these things would have changed significantly in the 10 or so generations since this audio was made seems quite out of the blue.
But if the bird has become significantly warier, doesn't it seem likely it could also have modified other behaviors as well?
I don't believe that it has. I think that is an ad hoc hypothesis that is unjustified and unnecessary. All you need is a bird of ordinary wariness (Pileateds don't like to be approached closely either) that is extremely rare and highly mobile. Throw one bird like that in a large area of forest, have them move many kilometers every day (Pileateds stay within a small home range), and have it be relatively quiet when it is not in the company of another member of its species (all these are behaviors that are justifiable with what we actually know), and I think you get the exact scenario we have been seeing. The only thing that has changed since the 19th century is a humongous decline in population. These reports of noisy obvious birds were generally on nesting territories and/or in areas where there were multiple interacting individuals. Some of the same people commented on how hard they were to find outside of the nesting season, or in areas where you didn't already know where the nests or roosts were.
I'm of two minds on the wariness question. It's certainly plausible that hunting pressure led warier birds to survive, and there's ample evidence that evolutionary changes can occur quite rapidly. At the same time, scarcity seems adequate to explain the difficulty we're facing in getting clear photos.
Most of the accounts of noisiness seem to pertain to vocalizations, and I would think that there's a difference between calling and drumming or rapping. I suspect that selection pressure would be greater with regard to the former than it would be with regard to the latter, especially (apparently) since no one has associated this rapping pattern with Ivory-bills until now. This take is purely intuitive.
MMinNY
I actually have a gut sort of feeling that these earlier researchers did recognize this loud, staccato pounding as Ivorybill, even if they never codified it as such. They seem to have deliberately included samples of it in the audio they archived, as though they were intending to document something characteristic of the species. It might not have been at the level of "steady rapping, 4-8 raps per second, 3-11 raps per series, slightly accelerating," more like just a recognition of "that sounds like an Ivorybill." I suspect any hunter who was seeking them would have learned to recognize it, too.
Bill, if slower rapping is the primary contact call, at least between members of a pair, as you suggest, would you propose that the kent call is something other than a contact call? I would think the latter might be the primary contact call -- but I am no expert on this.
Sorry, sloppy language, my bad. I meant just among the rapping sounds, the staccato pounding seems to have been more frequent than the fast double rap. Clearly that pair of birds used vocalizations as a very important contact feature as well.
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